1. Field of the Invention
The present invention relates to a liquid crystal display panel, and more particularly, to an apparatus for cutting a liquid crystal display panel to separate a plurality of unit liquid crystal display panels from a mother substrate.
2. Discussion of the Related Art
Generally, a liquid crystal display device provides liquid crystal cells arranged in a matrix form with corresponding data signals according to image information in order to display a desired image by controlling light-transmittance of each liquid crystal cell.
Accordingly, the liquid crystal display device is provided with a liquid crystal display panel where a plurality of liquid crystal cells of a unit pixel are arranged in a matrix form, and a driver integrated circuit for driving the liquid crystal cells of the liquid crystal display panel.
The liquid crystal display panel is composed of a color filter substrate and a thin film transistor array substrate attached to face to each other, and a liquid crystal layer filled between the two substrates.
On the thin film transistor array substrate of the liquid crystal display panel, a plurality of data lines for transmitting data signals supplied from a data driver integrated circuit to the liquid crystal cells are perpendicular to a plurality of gate lines for transmitting scan signals supplied from a gate driver integrated circuit to the liquid crystal cells. Herein, the liquid crystal cells are arranged at each intersection of the data lines and the gate lines.
The gate driver integrated circuit sequentially supplies the scan signals to the plurality of gate lines so that the liquid crystal cells arranged in a matrix form can be sequentially selected line by line. Also, the data signals are supplied to the liquid crystal cells of the selected one line from the data driver integrated circuit through a plurality of data lines.
In the meantime, a common electrode and a pixel electrode are respectively formed at the inner sides of the color filter substrate and the thin film transistor array substrate facing into each other, thereby applying an electric field to the liquid crystal layer. At this time, as opposed to the pixel electrode, which is formed correspondingly to each liquid crystal cell formed on the thin film transistor array substrate, the common electrode is integrally formed on the entire surface of the color filter substrate. Accordingly, light-transmittance of the liquid crystal cells can be individually controlled by controlling a voltage applied to the pixel electrode when a voltage is applied to the common electrode.
Similarly, a thin film transistor used as a switching device is formed at the respective liquid crystal cells in order to control the voltage applied to the pixel electrode formed on each liquid crystal cell.
Meanwhile, the thin film transistor array substrates are formed on a large mother substrate and the color filter substrates are formed on another mother substrate. The two mother substrates are then bonded, so that a plurality of liquid crystal display panels are formed at the same time to improve yield. Herein, a process for cutting the bonded substrates into unit liquid crystal display panels is required.
Generally, the cutting process of the unit liquid crystal display panels includes forming a scribing line at a surface of the mother substrate by a diamond wheel having a hardness greater than that of glass, and breaking the substrate by applying a mechanical force thereto. Hereinafter, a typical liquid crystal display panel will be explained with reference to the accompanied drawings.
FIG. 1 is a schematic view showing a related art unit liquid crystal display panel prepared by bonding a thin film transistor array substrate and a color filter substrate of the liquid crystal display device.
As shown in FIG. 1, a liquid crystal display panel 10 includes an image display unit 13 having liquid crystal cells arranged in a matrix form, a gate pad unit 14 connected to gate lines of the image display unit 13, and a data pad unit 15 connected to data lines. At this time, the gate pad unit 14 and the data pad unit 15 are formed on the end portions of a thin film transistor array substrate 1 which does not overlap with a color filter substrate 2. The gate pad unit 14 provides a scan signal supplied from a gate driver integrated circuit to the gate lines of the image display unit 13, and the data pad unit 15 provides image information supplied from a data driver integrated circuit to the data lines of the image display unit 13.
On the thin film transistor array substrate 1 of the image display unit 13, the data lines are arranged to be perpendicular to the gate lines. Then, thin film transistors are formed at each intersection to switch the liquid crystal cells. Pixel electrodes are connected to the thin film transistors to drive the liquid crystal cells. A passivation layer is formed on the entire surface of the thin film transistor array substrate 1 to protect the electrodes and the thin film transistors.
Also, the color filters separated by a black matrix for each cell area are formed on the color filter substrate 2 of the pixel display unit 13. Additionally, a transparent common electrode as a counter electrode of the pixel electrode is formed on the color filter substrate 2.
A cell gap is provided between the thin film transistor array substrate 1 and the color filter substrate 2, which are bonded to each other by a sealant (not shown) formed at the periphery of the image display unit 13, so as to be spaced apart from each other. A liquid crystal layer (not shown) is formed in the space between the thin film transistor array substrate 1 and the color filter substrate 2.
FIG. 2 is a cross-sectional view showing a first mother substrate having thin film transistor array substrates 1 and a second mother substrate having color filter substrates 2, wherein the first and second mother substrates are bonded to each other to form a plurality of liquid crystal display panels.
As shown in FIG. 2, each unit liquid crystal display panel has the end portions of the thin film transistor array substrate 1 protruding longer than the color filter substrate 2. This is because the gate pad unit 14 and the data pad unit 15 are formed at the end portions of the thin film transistor array substrate 1 which does not overlap with the color filter substrate 2.
Hence, the second mother substrate 30 and the color filter substrates 2 formed thereon are spaced apart from each other by a dummy region 31 corresponding to the protruding area of each thin film transistor array substrate 1 on the first mother substrate 20.
Moreover, the unit liquid crystal display panels are arranged so as to maximize the use of the first and second mother substrates 20 and 30. Although it may vary depending on the model, the unit liquid crystal display panels are generally spaced apart from each other at a distance corresponding to a second dummy region 32.
After the first mother substrate 20 having the thin film transistor array substrates 1 is bonded to the second mother substrate 30 having the color filter substrates 2, a scribing process and a breaking process are carried out to individually cut each of the liquid crystal display panels. In this case, the first dummy region 31 formed between each color filter substrate 2 of the second mother substrate 30 and the second dummy region 32 formed between each unit liquid crystal display panel are removed at the same time.
The related art cutting process of the unit liquid crystal display panels will be explained with reference to FIGS. 3A to 3J.
As shown in FIG. 3A, the first mother substrate 20 and the second mother substrate 30 bonded to each other are loaded on a first table 33.
Then, as shown in FIG. 3B, the first table 33 moves in one direction to a previously set distance to sequentially form a first scribing line 42 on the first mother substrate 20 through a cutting wheel 41.
Then, as shown in FIG. 3C, the first and second mother substrates 20 and 30 are turned by about 90°. The first table 33 moves back to its initial location at the previously set distance to sequentially form a second scribing line 43 on a surface of the first mother substrate 20 through the cutting wheel 41.
The cutting wheel 41 is bonded to the surface of the first mother substrate 20 with a constant pressure to be rotated, thereby forming the first and second scribing lines 42 and 43 having a groove on the surface of the first mother substrate 20.
Then, as shown in FIG. 3D, the first and second mother substrates 20 and 30 are overturned and are loaded on a second table 34. The second table 34 moves in one direction at a previously set distance, and propagates a crack on the first mother substrate 20 along the second scribing line 43 by pressing the second mother substrate 30 with a breaking rod 44.
As shown in FIG. 3E, after the second and first mother substrates 30 and 20 are turned by about 90°, the second table 34 moves back to its initial location at the previously set distance, and propagates a crack on the first mother substrate 20 along the first scribing line 42 by pressing the second mother substrate 30 with the breaking rod 44.
As shown in FIG. 3F, after the second and first mother substrates 30 and 20 are loaded on a third table 35, the third table 35 moves in one direction at a previously set distance to sequentially form a third scribing line 46 on the surface of the second mother substrate 30 through a cutting wheel 45.
As shown in FIG. 3G, the second and first mother substrates 30 and 20 are turned by about 90°, and the third table 35 moves back to the initial location at the previously set distance to sequentially form a fourth scribing line 47 on the surface of the second mother substrate 30 through the cutting wheel 45.
The cutting wheel 45 is bonded to the surface of the second mother substrate 30 with a constant pressure to be rotated, thereby forming the third and fourth scribing lines 46 and 47 having a groove on the surface of the second mother substrate 30.
As shown in FIG. 3H, the second and first mother substrates 30 and 20 are overturned to be loaded on a fourth table 36. The fourth table 36 moves in one direction at a previously set distance and propagates a crack on the second mother substrate 30 along the fourth scribing line 47 by pressing the first mother substrate 20 with a breaking rod 48.
As shown in FIG. 3I, after the first and second mother substrates 20 and 30 are turned by about 90°, the fourth table 36 moves back to the initial location at the previously set distance and propagates a crack on the second mother substrate 30 along the third scribing line 46 by pressing the first mother substrate 20 with the breaking rod 48.
As shown in FIG. 3J, the first and second mother substrates 20 and 30 are cut into unit liquid crystal display panels as the cracks are propagated along the first to fourth scribing lines 42, 43, 46, and 47 on the first and second mother substrates 20 and 30. The unit liquid crystal display panels are selectively unloaded using a suction plate 49 to be transferred to equipment for a later process.
In the related art apparatus for cutting liquid crystal display panels, when the scribing lines having a groove are formed on the surface of the substrate by bonding the cutting wheel to the surface of the substrate with a constant pressure and turning, glass debris are generated from a friction between the cutting wheel and the substrate.
When the glass debris are adhered to the surface of the substrate or the table on which the substrate is loaded, it causes a scratch or stain thereon.
The scratch or stain generated on the surface of the substrate deteriorates a picture quality of the liquid crystal display device, thereby increasing the defective proportions of a product and lowering productivity.